The world's biggest banks have to make up a slightly more than $2 trillion liquidity shortfall over the next four years to meet Basel III rules, says the Basel Committee on Banking Supervision. The committee also announced a change to the way "net stable funding ratio" would be calculated. Separately, the Committee of European Banking Supervisors released a study outlining the capital shortfall of Europe's 50 biggest banks. The forthcoming Basel rules call for banks to have their 30-day liquidity levels strengthened by 2014 and capital ratios meet the new standards by 2019.